/*
 * Copyright (c) "Neo4j"
 * Neo4j Sweden AB [http://neo4j.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.neo4j.gds.core.io.file;

import org.apache.commons.lang3.tuple.Pair;

import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

public class MappedListIterator<KEY, ENTRY> implements Iterator<Pair<KEY, ENTRY>> {

    private final Iterator<Map.Entry<KEY, List<ENTRY>>> mapEntryIterator;
    private Iterator<ENTRY> listEntryIterator;
    private KEY currentKey;

    public MappedListIterator(Map<KEY, List<ENTRY>> mappedList) {
        this.mapEntryIterator = mappedList.entrySet().iterator();
        if (mapEntryIterator.hasNext()) {
            Map.Entry<KEY, List<ENTRY>> mapEntry = mapEntryIterator.next();
            currentKey = mapEntry.getKey();
            listEntryIterator = mapEntry.getValue().listIterator();
        } else {
            listEntryIterator = Collections.emptyListIterator();
        }
    }

    @Override
    public boolean hasNext() {
        while (!listEntryIterator.hasNext()) {
            if (!mapEntryIterator.hasNext()) {
                return false;
            }
            Map.Entry<KEY, List<ENTRY>> mapEntry = mapEntryIterator.next();
            currentKey = mapEntry.getKey();
            listEntryIterator = mapEntry.getValue().listIterator();
        }
        return true;
    }

    @Override
    public Pair<KEY, ENTRY> next() {
        return Pair.of(currentKey, listEntryIterator.next());
    }
}
